Cataract extraction is one of the most commonly performed surgical procedures in the world. A cataract is formed by opacification of the crystalline lens or its envelope—the lens capsule—of the eye. A cataract obstructs passage of light through the lens. A cataract can vary in degree from slight to complete opacity. Early in the development of an age-related cataract the power of the lens may be increased, causing near-sightedness (myopia). Gradual yellowing and opacification of the lens may reduce the perception of blue colors as those wavelengths are absorbed and scattered within the crystalline lens. Cataract formation typically progresses slowly resulting in progressive vision loss. Cataracts are potentially blinding if untreated.
A common cataract treatment involves replacing the opaque crystalline lens with an artificial intraocular lens (IOL). Presently, an estimated 15 million cataract surgeries per year are performed worldwide. The cataract treatment market is composed of various segments including intraocular lenses for implantation, viscoelastic polymers to facilitate surgical maneuvers, and disposable instrumentation including ultrasonic phacoemulsification tips, tubing, various knives, and forceps.
Presently, cataract surgery is typically performed using a technique termed phacoemulsification in which an ultrasonic tip with associated irrigation and aspiration ports is used to sculpt the relatively hard nucleus of the lens to facilitate its removal through an opening made in the lens anterior capsule. The nucleus of the lens is contained within an outer membrane of the lens that is referred to as the lens capsule. Access to the lens nucleus can be provided by performing an anterior capsulotomy in which an opening is formed in the anterior side of the lens capsule. Access to the lens nucleus can also be provided by performing a manual continuous curvilinear capsulorhexis (CCC) procedure, which has been recently developed. After removal of the lens nucleus, a synthetic foldable intraocular lens (IOL) can be inserted into the remaining lens capsule of the eye through a small incision. Typically, the IOL is held in place by the lens anterior capsule. The IOL may also be held by the lens posterior capsule, either alone or in unison with the lens anterior capsule. This latter configuration is known in the field as a “bag-in-lens” implant.
One of the most technically challenging and critical steps in the cataract extraction procedure is providing access to the lens nucleus. The manual continuous curvilinear capsulorhexis (CCC) procedure evolved from an earlier technique termed can-opener capsulotomy in which a sharp needle was used to perforate the lens anterior capsule in a circular fashion followed by the removal of a circular fragment of lens anterior capsule typically in the range of 5-8 mm in diameter. The smaller the capsulotomy, the more difficult it is to produce manually. The capsulotomy facilitates the next step of nuclear sculpting by phacoemulsification. Due to a variety of complications associated with the initial can-opener technique, attempts were made by leading experts in the field to develop a better technique for forming an opening in the lens anterior capsule preceding the emulsification step.
The desired outcome of the manual continuous curvilinear capsulorhexis is to provide a smooth continuous circular opening through which not only the phacoemulsification of the nucleus can be performed safely and easily, but also to provide for easy insertion of the intraocular lens. The resulting opening in the lens anterior capsule provides both a clear central access for tool insertion during removal of the nucleus and for IOL insertion, a permanent aperture for transmission of the image to the retina by the patient, and also support of the IOL inside the remaining capsule that limits the potential for dislocation. The resulting reliance on the shape, symmetry, uniformity, and strength of the remaining capsule to contain, constrain, position, and maintain the IOL in the patient's eye limits the placement accuracy of the IOL, both initially and over time. Subsequently, a patient's refractive outcome and resultant visual acuity are less deterministic and intrinsically sub-optimal due to the IOL placement uncertainty. This is especially true for astigmatism correcting (“toric”) and accommodating (“presbyopic”) IOLs.
Problems may also develop related to inability of the surgeon to adequately visualize the lens capsule due to lack of red reflex, to grasp the lens capsule with sufficient security, and to tear a smooth circular opening in the lens capsule of the appropriate size and in the correct location without creating radial rips and extensions. Also present are technical difficulties related to maintenance of the depth of the anterior chamber after opening the lens capsule, small pupil size, and/or the absence of a red reflex due to lens opacity. Some of the problems with visualization can be minimized through the use of dyes such as methylene blue or indocyanine green. Additional complications may also arise in patients with weak zonules (typically older patients) and very young children that have very soft and elastic capsules, which are very difficult to controllably and reliably rupture and tear.
The implantation of a “bag-in-lens” IOL typically uses anterior and posterior openings in the lens capsule of the same size. Manually creating matching capsulotomies for the “bag-in-lens” configuration, however, is particularly difficult.
Many cataract patients have astigmatic visual errors. Astigmatism can occur when the corneal curvature is unequal in all directions. IOLs can be used to correct for astigmatism but require precise rotational and central placement. Additionally, IOLs are not typically used for correction beyond 5D of astigmatism. Many patients, however, have astigmatic visual errors exceeding 5D. Higher correction beyond 5D typically requires reshaping the cornea to make it more spherical. There are numerous existing approaches for reshaping the cornea, including Corneaplasty, Astigmatic Keratotomy, Corneal Relaxing Incision (CRI), and Limbal Relaxing Incision (LRI). In Astigmatic Keratotomy, Corneal Relaxing Incision (CRI), and Limbal Relaxing Incision (LRI), corneal incisions are made in a well-defined manner and depth to allow the cornea to change shape to become more spherical. Presently, these corneal incisions are typically accomplished manually often with limited precision.
Thus, improved methods and systems for treating cataracts are needed.